BST-927 9 in 1 Mini Screwdriver Pen Set Aluminum Alloy Handle S2 Screw Bits Professinal design, beauty appearance and portable screwdriver set is easy to use Multipoint and adjustable extension bar is easy to disassemble and can be changed the length according to different requirements High quality and precision screw heads of all types are suitable for work in different areas The handle of ergonomic design is easy to operate. Precision screw heads under high temperature processing are made of high quality chrome- vanadium steel (6150#),whose HRC is from 52-56 degree.